I think alot of it has to do with our society- and ignorance. Cycling has always seemed like a "fringe" sport here in the states, and I think certain sectors of society think we are freaks. Of course in my experience it's been the macho types that feel they need to feed their ego. I've also noticed that it depends alot on where you live. In nor cal there seemed to be alot of animosity by people that lived in the country because of having to fight the packs that ride 3-4 abreast on the weekends. I grew up in the country and I've dealt with it myself. You are going down a country road and all the sudden you come upon a club ride and they are riding like they're in the peloton at tdf- god forbid they move over to ride single file. I guess that comes w/ societies general feeling of entitlement. As if they are entitled to the entire road. Of course alot of drivers suffer from the entitlement complex as well. So I guess it's a double edged sword...
Now that I've moved to AZ it's totally different. In our area there are alot of active people, so I'm always waved through stop signs, given a wide berth etc. I've noticed when I ride up here that the only people I have trouble with are the construction workers.
I think the answer is to convert as many people to biking as possible! The more that understand our point of view the better it will be for all!
Of course as cyclists we have an obligation to follow the rules of the road as well.